Solid-state imaging device, production method of the same, and imaging apparatus

ABSTRACT

In a solid-state imaging device, the pixel circuit formed on the first surface side of the semiconductor substrate is shared by a plurality of light reception regions. The second surface side of the semiconductor substrate is made the light incident side of the light reception regions. The second surface side regions of the light reception regions formed in the second surface side part of the semiconductor substrate are arranged at approximately even intervals and the first surface side regions of the light reception regions formed in the first surface side part of the semiconductor substrate are arranged at uneven intervals, respectively, and the second surface side regions and the first surface side regions are joined respectively in the semiconductor substrate so that the light reception regions extend from the second surface side to the first surface side of the semiconductor substrate.

CROSS REFERENCES TO RELATED APPLICATIONS

The invention contains subject matter related to Japanese PatentApplication JP 2007-138081 filed in the Japanese Patent Office on May24, 2007, the entire contents of which being incorporated herein byreference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention relates to a solid-state imaging device with a CMOS sensorfor example, a production method of the same, and an imaging apparatus.

2. Description of the Related Art

Recently, for the purpose of installing a camera function in a mobileapparatus such as a mobile phone, etc., demand for making a solid-stateimaging device compact is increasing.

In a solid-state imaging device such as a CMOS image sensor, etc.,generally a structure is adopted in which photodiodes (PDs) are arrangedat constant intervals, for example, in a square lattice to sampleincident light.

Therefore, the problem is arising that with downsizing of thesolid-state imaging device as described above and miniaturization of theunit pixel due to the increase in the number of pixels, the area of a PDdecreases and the characteristics of the solid-state imaging device,such as the saturation signal amount, the sensitivity, etc., decreases.

In the past, to prevent such decrease in the characteristics of thesolid-state imaging device, a method has been adopted in which thedecrease in the area of the PD is suppressed by decreasing the area oftransistors in a unit pixel. However, there is a limit in keeping thecharacteristics of the solid-state imaging device with the method ofkeeping the area of the PD by decreasing the area of the transistors.

Japanese Unexamined Patent Application Publications No. 63-100879 andNo. 2004-128193 describe a CMOS image sensor in which a pixel circuitother than the PD and the charge-transfer transistor are shared byneighboring unit pixels (see, for example, page 4, FIG. 4 of JP No.63-100879 and paragraph numbers [0019]-[0040] and FIG. 2 of JP No.2004-128193).

In the above-described CMOS image sensor, the number of transistors andthe number of wirings per a unit pixel can be decreased, and as aresult, a relatively large area can be secured for the PD, so that it ispossible to cope with the miniaturization of the unit pixel.

SUMMARY OF THE INVENTION

However, in the structure described in the above-described JPPublications, in each unit pixel, a PD and a circuit region that isshared by neighboring unit pixels are mixed. In this case, because theshared region is arranged between neighboring unit pixels, the relativepositions PDs occupy in the neighboring unit pixels generally differbetween the neighboring unit pixels.

As a result, in the planar configuration, the PDs are arranged not in asquare lattice but at uneven intervals.

When PDs are not arranged at even intervals, incident light is sampled,spatially at uneven intervals. In this case, the following problemsarise.

a) The need to correct the sampled signal arises, so that as comparedwith the case that PDs are arranged at even intervals, signal processingbecomes complicated.

b) If the arrangement of PDs differs depending on the type of the CMOSsensor, signal processing also has to be changed accordingly.

c) When an image with lights and darks in a stripe pattern is imaged,especially when the extending direction of stripes is oblique relativeto the arrangement of pixels, it becomes difficult to reproduceintervals, colors, etc. of the stripes.

d) Because usual signal processing ICs are designed on the assumptionthat sampling is carried out at even intervals, it is highly likely thattypical signal processing ICs may not be used and system structure islimited.

e) In the pixels in the periphery parts far from the optical axis, lightis obliquely incident, so that the output manner of shading is caused todiffer due to the arrangement at uneven intervals of the PDs. Forexample, even when a white subject is imaged, an upper edge and a loweredge thereof are colored and in addition, are colored in differentcolors, so that correction of the shading becomes difficult.

Because the above-described inconveniences arise, it is preferable thatsampling of the incident light is carried out at even intervals.

To solve the above-described problems, in the past, the followingmethods have been taken.

1) Arranging transistors evenly around a PD so that PDs are arranged ateven intervals

2) Providing an extra space so that PDs are arranged at even intervals

3) With respect to PDs arranged at uneven intervals, adequatelynarrowing the optical opening and arranging light incident regions ateven intervals

With respect to the above-described method 1), in almost all of varioussolid-state imaging devices such as a CMOS sensor, etc., because it isextremely difficult to arrange PDs at completely equal intervals, itresults in reducing the area of the PDs and decreasing thecharacteristics of pixel circuits such as conversion gain, etc.

With respect to the above-described method 2), similarly, it results inreducing the area of the PDs and decreasing the characteristics of pixelcircuits.

In the above-described method 3), there is an inconvenience thatsensitivity is caused to fall.

As another example of a CMOS sensor, the applicant has proposed arear-surface-incident-type CMOS sensor in Japanese Unexamined PatentApplication Publication No. 2003-31785. The proposedrear-surface-incident-type CMOS sensor receives light from the rear sideas illustrated in FIG. 1.

In FIG. 1, by polishing a substrate made of silicon, etc. by means ofCMP (Chemical Mechanical Polishing), a silicon part 204 about 10-20 μmthick is formed. Gate electrodes 212 and wiring layers 211 are formed onone surface (i.e., the front surface) side of the silicon part 204 viaan interlayer insulating layer and thereby a gate/wiring part 203 isformed. Further, a support substrate 201 is joined on the gate/wiringpart 203 by means of an adhesive 202. Color filters 206 and on-chiplenses 207 are formed on the other surface (the rear surface) side ofthe silicon part 204 while sandwiching a SiO₂ film 205.

In the silicon part 204, impurity regions 214 of n-type for example,which become source and drain regions of the gate electrodes 212, andphotoelectric conversion regions 213, each including a p-type impurityregion and an n-type impurity region constituting a PD, are formed, andimpurity regions 205 of n-type for example, which become light incidentregions, are formed on the rear surface side of the silicon part 204 tobe connected with the n-type impurity regions of the photoelectricconversion regions 213. Further, a p-type impurity region 216 is formedthroughout on the surface on the rear surface side of the silicon part204.

With the above-described configuration, in contrast to that in CMOSsensors in related art, a pixel structure of afront-surface-incident-type has been adopted, in which, the wiring layerside is made the front surface side and the incident light is taken infrom the wiring layer side, in the example illustrated in FIG. 1, theincident light is taken in from the surface side opposite the wiringlayer 211 (i.e., rear surface side), that is, the rear-surface-incidenttype structure is adopted. When the rear-surface-incident-type structureis adopted, as apparent from the incident light indicated by arrows 200and the pixel structure, it is possible to avoid restriction incondensing due to vignetting at the wiring layers 211 and to therebyenhance condensing efficiency.

However, in the rear-surface-incident-type structure, only the designsin which PDs are arranged at even intervals are known. This is becausethat unless the PDs are arranged at even intervals, the above-describedproblems occur. Therefore, it is difficult to achieve both sharing ofpixel circuits and arranging PDs at even intervals, as in the case offront-surface-incident-type structure.

The invention was conceived in view of the above-described and otherproblems and addresses avoiding, when pixel circuits are shared by aplurality of light reception regions, signal processing from becomingcomplicated due to the arrangement of the light reception regions atuneven intervals.

According to an embodiment of the invention, a solid-state imagingdevice includes a semiconductor substrate with a first surface and asecond surface opposite the first surface, a plurality of lightreception regions formed in the semiconductor substrate, respectivelyhaving first surface side regions formed in a first surface side part ofthe semiconductor substrate and second surface side regions formed in asecond surface side part of the semiconductor substrate, and a pixelcircuit formed on the first surface side of the semiconductor substrateand shared by the plurality of light reception regions. The secondsurface side, opposite the first surface side where the pixel circuit isformed, of the semiconductor substrate is made a light incident side ofthe light reception regions. The second surface side regions of thelight reception regions formed in the second surface side part of thesemiconductor substrate are arranged at approximately even intervals andthe first surface side regions of the light reception regions formed inthe first surface side part of the semiconductor substrate are arrangedat uneven intervals, respectively, and the second surface side regionsand the first surface side regions of the light reception regions arejoined respectively in the semiconductor substrate so that the lightreception regions extend from the second surface side to the firstsurface side of the semiconductor substrate.

According to another embodiment of the invention, an imaging apparatusincludes a solid-state imaging device, an imaging optical unit guidinglight from an imaging subject to the solid-state imaging device, and asignal processing unit processing an image signal outputted from thesolid-state imaging device. The solid-state imaging device includes asemiconductor substrate with a first surface and a second surfaceopposite the first surface, a plurality of light reception regionsformed in the semiconductor substrate, respectively having first surfaceside regions formed in a first surface side part of the semiconductorsubstrate and second surface side regions formed in a second surfaceside part of the semiconductor substrate, and a pixel circuit formed onthe first surface side of the semiconductor substrate and shared by theplurality of light reception regions. The second surface side, oppositethe first surface side where the pixel circuit is formed, of thesemiconductor substrate is made a light incident side of the lightreception regions. The second surface side regions of the lightreception regions formed in the second surface side part of thesemiconductor substrate are arranged at approximately even intervals andthe first surface side regions of the light reception regions formed inthe first surface side part of the semiconductor substrate are arrangedat uneven intervals, respectively, and the second surface side regionsand the first surface side regions of the light reception regions arejoined respectively in the semiconductor substrate so that the lightreception regions extend from the second surface side to the firstsurface side of the semiconductor substrate.

According to still another embodiment of the invention, a productionmethod of a solid-state imaging device is provided. The productionmethod includes steps of; implanting impurity of a firstconductivity-type from a first surface side of a semiconductor substrateto form second surface side regions of light reception regions atapproximately even intervals in a second surface side part of thesemiconductor substrate; forming device separation regions in a firstsurface side part of the semiconductor substrate; forming gateelectrodes on the first surface of the semiconductor substrate;implanting second conductivity-type impurity on the second surface sideregions of the light reception regions from the first surface side ofthe semiconductor substrate to form first surface side regions of thelight reception regions at uneven intervals in the first surface sidepart of the semiconductor substrate; forming an interlayer insulatinglayer and wiring layers on the first surface of the semiconductorsubstrate; and etching the semiconductor substrate from the secondsurface side opposite the first surface of the semiconductor substrateto expose the second surface side regions of the light reception regionsarranged at approximately even intervals in the second surface side partof the semiconductor substrate. The step of implanting impurity from thefirst surface side of the semiconductor substrate to form the secondsurface side regions of the light reception regions is carried outbefore the step of forming the device separation regions.

As described above, in the solid-state imaging device and the imagingapparatus according to embodiments of the invention, a pixel circuit isshared by a plurality of light reception regions, and the solid-stateimaging device is configured as a rear-surface-incident type device thatthe second surface side, opposite the first surface side where the pixelcircuit is formed, of the semiconductor substrate is made a lightincident side of the light reception regions. In particular, the firstsurface side of the light reception regions are arranged at unevenintervals in the first surface side part of the semiconductor substrateso that the pixel circuit to be formed on the first surface side of thesemiconductor substrate can be arranged relatively reasonably, and atthe same time, the second surface side regions of the light receptionregions are arranged at approximately even intervals in the secondsurface side part of the semiconductor substrate. That is, the secondsurface side regions and the first surface side regions of the lightreception regions are joined respectively in the semiconductor substrateso that the light reception regions extend from the second surface sideto the first surface side of the semiconductor substrate. In otherwords, in the semiconductor substrate, respective light receptionregions are formed so as to extend from the second surface side to thefirst surface side of the semiconductor substrate in shapes differentfrom those of neighboring light reception regions, and they are arrangedat uneven intervals on the first surface side of the semiconductorsubstrate and at approximately even intervals on the second surface sideof the semiconductor substrate, respectively, and thereby deterioratingimage quality and introducing complexity to signal processing can beavoided.

Further, according to the production method of the solid-state imagingdevice according to an embodiment of the invention, the solid-stateimaging device with the above-described configuration can be relativelyeasily produced. In particular, because the second surface side regionsof the light reception regions, which become the light incident regionson the rear surface side of the semiconductor substrate, are formed byimplanting impurity from the first surface side of the semiconductorsubstrate in the relatively early step, the variation in the density ofthe impurity in the regions can be suppressed by diffusing the impurityin the subsequent heating step. Further, by carrying out the step ofimplanting the first conductivity-type impurity from the first surfaceside of the semiconductor substrate before the step of forming thedevice separation regions, the impurity does not pass the deviceseparation regions, so that the second surface side regions of the lightreception regions as the light incident regions can be formed in moreuniform impurity density.

According to the solid-state imaging device and the imaging apparatusaccording to embodiments of the invention, in the case that a pixelcircuit is shared by a plurality of light reception regions,deterioration of image quality and complication of signal processing dueto that the light reception regions are arranged at uneven intervals canbe avoided.

Further, according to the production method of the solid-state imagingdevice according to an embodiment of the invention, the solid-stateimaging device avoiding signal processing from becoming complicated canbe produced relatively easily, and in particular, it becomes possible tosuppress variation in the impurity density in the impurity regionsconstituting the light reception regions.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic cross section illustrating a construction of anexisting rear-surface-incident-type solid-state imaging device.

FIG. 2 is a schematic planer view of a solid-state imaging deviceaccording to an embodiment of the invention.

FIG. 3 is a schematic configuration diagram of a pixel circuit of thesolid-state imaging device.

FIG. 4 is a schematic planer view illustrating an exemplaryconfiguration of the solid-state imaging device when the pixel circuitillustrated in FIG. 3 is laid out on a planer surface.

FIG. 5A is a schematic planer view of a part of the planer view of FIG.4.

FIG. 5B is a cross section on an AA′ line in FIG. 5A.

FIG. 6A, FIG. 6B, and FIG. 6C are production process diagrams of a firstpart of a production method of the solid-state imaging device accordingto an embodiment of the invention.

FIG. 7A, FIG. 7B and FIG. 7C are production process diagrams of a secondpart of the production method of the solid-state imaging device.

FIG. 8 is a production process diagram of a third part of the productionmethod of the solid-state imaging device.

FIG. 9 is a production process diagram of a fourth part of theproduction method of the solid-state imaging device.

FIG. 10 is a production process diagram of a fifth part of theproduction method of the solid-state imaging device.

FIG. 11 is a schematic planer configuration diagram of a principal partof the solid-state imaging device according to another embodiment of theinvention.

FIG. 12 is a schematic planer configuration diagram of a principal partof the solid-state imaging device according to another embodiment of theinvention.

FIG. 13 is a schematic planer configuration diagram of a pixel part ofthe solid-state imaging device according to another embodiment of theinvention.

FIG. 14 is a schematic planer configuration diagram of a pixel part ofthe solid-state imaging device according to another embodiment of theinvention.

FIG. 15 is a schematic planer configuration diagram of a pixel part ofthe solid-state imaging device according to another embodiment of theinvention.

FIG. 16 is a schematic configuration diagram of an imaging apparatusaccording to an embodiment of the invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Example of preferred embodiments of the invention will now be describedwith reference to drawings. The invention is not limited to the examplesdescribed below.

FIG. 2 is a schematic plan view of a solid-state imaging deviceaccording to an embodiment of the invention. As illustrated in FIG. 2, asolid-state imaging device 10 includes a pixel part 1, a vertical drivecircuit 2, a column circuit 3, a horizontal drive circuit 4, a controlcircuit 5, a horizontal bus 6, and an output circuit 7. These parts aremounted on a substrate (not shown).

In the pixel part 1, a number of pixels are arranged in a line-columnstate. Further, a pixel drive wiring (not shown) extending in the linedirection is arranged for each line of pixels, and a vertical signalline (now shown) extending in the column direction is arranged for eachcolumn of pixels.

Respective pixels of the pixel part 1 are driven by the pixel drivewiring. The signal for the pixel is an analog signal and is outputted tothe vertical signal line.

The control circuit 5 receives input clocks, and data instructing anoperation mode, etc., and outputs data such as internal information ofthe solid-state imaging device 10. Further, the control circuit 4supplies clocks and pulses necessary for driving the vertical drivecircuit 2, the horizontal circuit 4, the column unit 3, and the outputcircuit 7.

The vertical drive circuit 2 selects a pixel drive wiring, and suppliespulses for driving pixels to the selected pixel drive wiring. By drivinga pixel drive wiring, pixels of one line associated with the pixel drivewiring are simultaneously driven.

In the column unit 3, columns circuits are arranged to correspond to thecolumns of pixels. The column circuits take in pixel signals ofrespective columns in the pixel part 1 from the vertical signal lines ofthe pixel part 1. The column unit 3 carries out CDS (Correlated DoubleSampling), which is fixed-pattern noise removing processing, signalamplification processing, AD conversion processing, etc. on the taken-inpixel signals.

The horizontal drive circuit 4 sequentially selects column circuits ofthe column unit 3, and guides the signals held in the column circuits tothe horizontal bus 6.

The output circuit 7 processes the signals from the horizontal bus 6 andoutputs the processed signals. For example, sometimes only buffering iscarried out, and sometimes processes are carried out, such as blacklevel adjustment, column variation correction, various types of digitalsignal processing, etc.

FIG. 3 illustrates an exemplary structure of a pixel circuit in a pixelof the solid-state imaging device 10. In this example, four sets of alight reception unit 61 (61 a-61 d), each including a photodiode (PD),etc. and constituting a light reception region, and a transfertransistor 62 (62 a-42 d) share a set of a reset transistor 67, anamplification transistor 64, and a selection transistor 65, constitutinga pixel circuit.

The light reception units 61 a-61 d including PDs, etc. as photoelectricconversion elements are connected with a floating diffusion (FD) 63 viathe transfer transistors 62 a-62 d, respectively. The floating diffusion63 is a node including two diffusion layers corresponding to drains ofthe transfer transistors 62 a-62 d, gates of the amplificationtransistor 64, and a wiring connecting these diffusion layers and gates.The transfer transistors 62 a-62 d transfer photoelectrons of the lightreception units 61 a-61 d to the floating diffusion 63. Because thevoltage of the gates of the amplification transistor 64 is the one ofthe floating diffusion 63, if the selection transistor 65 is turned on,the amplification transistor 64 outputs a signal corresponding to thepotential of the floating diffusion 63 to the vertical signal line 68.The reset transistor 67 resets the floating diffusion 63 by dischargingthe electrons of the floating diffusion 53 to a power source (Vdd)wiring 66.

FIG. 4 illustrates an exemplary configuration of the solid-state imagingdevice 10 when the pixel circuit illustrated in FIG. 3 is laid out on aplaner surface. Here, for the sake of the viewability, metal wiringsother than wirings 69 of the floating diffusion 63 and contacts betweenmetal wirings are omitted. In FIG. 4, the direction of lines in FIG. 2is indicated by an arrow x and the direction of columns in FIG. 2 isindicated by an arrow y. As illustrated in FIG. 4, the pair of the lightreception units 61 a, 61 b and the pair of the light reception units 61c, 61 d are respectively arranged substantially symmetrically in thecolumn direction indicated by the arrow y, and the floating diffusion63, the reset transistor 67, contact units 70, and the transfertransistors 62 a, 62 b, 62 c, 62 d of the light reception units 61 a, 61b, 61 c, 61 d are disposed between the light reception units 61 a, 61 b,61 c, 61 d thus arranged. Specifically, they are disposed between thelight reception unit 61 a and the light reception unit 61 b and betweenthe light reception unit 61 c and the light reception unit 61 d, thatis, in every other in-between space of light reception units withrespect to the column direction. In this case, an interval D1 of thelight reception unit 61 b and the light reception unit 61 c and aninterval D2 of the light reception unit 61 c and the light receptionunit 61 d are different, so that the light reception units are arrangedat uneven interval.

The cross section structure of the pixel circuit is described referringto FIG. 5A and FIG. 5B. FIG. 5A illustrates a part of the schematicplaner diagram of FIG. 4, and FIG. 5B illustrates a cross sectionstructure at an AA′ line of FIG. 5A. In FIG. 5A and FIG. 5B, the partscorresponding to those in FIG. 4 are denoted by the same referencesymbols and overlapped description is omitted. In FIG. 5A, for theconvenience sake, the planar structure diagram illustrated in FIG. 4 isrotated 90 degrees transversely. In FIG. 5B, the wirings, the supportsubstrate, the color filter, the on-chip lens, etc. are omitted and onlya semiconductor substrate 11 consisted of silicon, etc., and thetransfer transistors 62 a-62 d are illustrated.

The invention is characterized in that the shapes in the depth directionof the light reception units 61 a-61 d are made different betweenneighboring pixels. In the illustrated example, in the part on the firstsurface 11A side where pixel circuits are formed of a semiconductorsubstrate 11, second conductivity-type impurity regions 21 a-21 d forexample of p-type and first-type impurity regions 20 a-20 d for exampleof n-type are formed at uneven intervals separated by device separationregions 18, as first surface side regions of the light receptionregions. On the other hand, in the part on the second surface 11B side,which is on the opposite side of the first surface 11A side where pixelcircuits are formed and which is on the light incident side, of thesemiconductor substrate 11, first conductivity-type impurity regions 17a-17 d for example of n⁻-type of relatively low density, which areconnected with the first conductivity-type impurity regions 20 a-20 d,are formed at uneven intervals, as second surface side regions of thelight reception regions, and thereby the light reception regions 61 a-61d are formed.

At this time, as indicated by broken lines Ca-Cd, junction parts of thefirst surface 11A side regions, i.e., the second conductivity-typeimpurity regions 21 a-21 d and the first-type impurity regions 20 a-20d, and the second surface 11B side regions, i.e., the firstconductivity-type impurity regions 17 a-17 d, of the light receptionunits 61 a-61 d are differently shaped depending on the arrangementpositions of the impurity regions in the first surface 11A side part andthe arrangement positions of the impurity regions in the second surface11B side part. That is, in this example, the junction parts Ca-Cd areformed differently in junction position and area between neighboringpixels, so to say, within the semiconductor substrate 11, impurityregions are connected with each other while being bent. By thusselecting the injunction positions appropriately, the light receptionunits 61 a-61 d can be arranged at approximately even intervals in thesecond surface 11B side part of the semiconductor substrate 11, which isthe light incident side, even if the arrangement thereof is at uneveninterval in the first surface 11A side part, so that spatial sampling ofpixels is carried out approximately at even intervals.

Accordingly, the problems that have been addressed in the past either bysacrificing the characteristics of pixels or by bending the optical pathare solved in the invention by bending the path of photo-electricallyconverted electrons pixel by pixel.

It should be noted that the number of layers of impurity regions is notlimited to the illustrated one, and can be two or four or more. However,it is preferable that the junction surfaces of the p-type regions andthe n-type regions have approximately the same shape and area inrespective pixels. Further, the p-type and the n-type may be reversed.

When the structures in the depth direction of the light reception unitsare different between neighboring pixels, there is a possibility thatshading occurs depending on the difference of the structures. That is,in FIG. 5B, when light enters at a slanted angle from the second surface11B side as indicated by arrows La-Ld, depending on the difference inthe relative positions between the first conductivity-type impurityregions 17 a-17 d and the junction parts surrounded by the broken linesCa-Cd, there is a possibility that the light reaches or the light doesnot reach the first conductivity-type impurity regions 20 a-20 d on thefirst conductivity-type impurity regions 17 a-17 d. In the illustratedexample, the light does not reach the first conductivity-type impurityregions 20 c and 20 d as indicated by the tip ends of the arrows Lc andLd in the regions 20 c and 20 d.

To avoid such variation, it is important that photoelectrical conversionis sufficiently performed in the first conductivity-type impurityregions 17 a-17 d arranged at approximately even intervals in the secondsurface 11B side part of the semiconductor substrate 11 and that a largeamount of light does not pass through the regions 17 a-17 d. Therefore,it is preferable that the first conductivity-type impurity regions 17a-17 d extend 1 μm or more from the second surface 11B in the depthdirection of the semiconductor substrate 11. Further, to deplete theregions 17 a-17 d to transmit photo-electrically converted electrons tothe first surface 11A side by an electric field, it is preferable that adepth “ts” from the second surface 11B is 5 μm or less.

Next, a production method of the solid-state imaging device 10 accordingto an embodiment of the invention is described referring to productionprocess diagrams of FIG. 6A through FIG. 10. Description will be madeonly with respect to the principal points taking a part of the regionsillustrated in FIG. 5B as an example.

Process (1):

This example is the case that a SOI (Semiconductor On Insulator)substrate is used, and as illustrated in FIG. 6A, a silicon part, whichis formed on a substrate 13 consisted of silicon, etc. through aninsulating film 12 consisted of an embedded oxide film, etc., may beused as a semiconductor substrate 11. That is, the semiconductorsubstrate in the solid-state imaging device according to an embodimentof the invention may be a semiconductor region provided in a part of asubstrate. A thickness “t” of the silicon part when the SOI substrate isused, i.e., the semiconductor substrate 11, is preferably relativelythick, for example, about 4 μm, and the semiconductor substrate 11 canbe the first conductivity-type of low impurity density about 10¹⁵ cm⁻³,for example, n⁻⁻-type.

After thinly forming an insulating film 14 by thermal oxidation on thesurface of the semiconductor substrate 11, second conductivity-typeimpurity regions 15 are formed for example in the region 1.8 μm deep ormore by implanting, for example, boron, etc., which is p-type impurity.When carrying out ion implantation to a relatively deep region from thesurface, it is preferable to use a high-energy ion implantationapparatus capable of handling mega electron volt. The secondconductivity-type impurity regions 15 are formed with its planer shapebeing made, for example, in a lattice shape and are arranged at evenintervals.

Process (2):

As illustrated in FIG. 6B, in the region 1.8 μm deep or more from thefirst surface 11A of the semiconductor substrate 11, secondconductivity-type impurity such as boron, etc. is implanted whileavoiding the regions that will become the upper parts, i.e., firstsurface 11A side regions, of the light reception units in subsequentprocesses, and thereby second conductivity-type impurity regions 16 tobe connected with the second conductivity-type impurity regions 15 areformed.

Because the first surface side regions of the light reception units areto be arranged at uneven intervals, the junction parts with the secondconductivity-type impurity regions 15 in the deep position implanted inthe above-described Process (1) are different in shapes, i.e., differentin junction positions and in junction areas, between neighboring pixels.

Process (3):

Next, as illustrated in FIG. 6C, in the region in the depth not reachingthe insulating layer 14, i.e., in the depth from about 1.8 μm to about3.5 μm from the first surface 11A, first conductivity-type impurityregions 17 of n⁻-type, which will become the lower parts, i.e., secondsurface 11B side regions, of the light reception units, are formed bycarrying out ion implantation of first conductivity-type impurity ofn-type. In this case also, impurity implantation is carried out using ahigh-energy ion implantation apparatus capable of handling mega electronvolt as in the above-described second conductivity-type impurity regions15.

This ion implantation is carried out to the opening parts of the latticeshape of the first conductivity-type impurity regions 15 formed in theabove-described Process (1), so that the first conductivity-typeimpurity regions 17 are arranged at even intervals.

However, in this case, because the configurations of the pixels in thefirst surface 11A side regions are different between neighboring pixels,damages to the vicinity of the surfaces of the pixels due to ionimplantation differ between the neighboring pixels. Therefore, so as toreduce the difference in the degrees of damages to the vicinity of thesurfaces of pixels between neighboring pixels, as the ion for use in theion implantation, the one with small atomic weight, for example,phosphorus is preferably used.

On the other hand, to collect the electrons to the first surface 11Aside of the light reception units, that is, to the wiring circuit side,it is preferable to configure such that the impurity density increasestoward the first surface 11A side. Therefore, it is suitable to ionimplant while increasing the dosing amount several times toward thefirst surface 11A side.

Here, with respect to ion implanting to such a deep region, a method isalso conceivable to ion implant, after once exposing the second surface11B, i.e., the rear surface, from the rear surface side with relativelylow energy. However, in the present embodiment, in the above-describedProcess (3), ion implantation is carried out from the first surface 11Aside, i.e., from the front surface side of the semiconductor substrate11, with relatively high energy. The reasons for that are as follows.

In the solid-state imaging device according to an embodiment of theinvention, the junction positions of the first surface side regions andthe second surface side regions of the light reception units aredifferent between neighboring pixels. Because of this, if a differenceexists locally in the density of impurity such as phosphorus, etc.,there is a possibility that variation is caused in sensitivity,saturation, afterimage, etc. between neighboring pixels. To avoid orsuppress such variation, it is preferable to diffuse impurity more afterion implantation so that the local density difference becomes small andthe density distribution becomes gentle. To achieve this, a relativelystrong heating process is to be applied after implantation, however, ifsuch a heating process is applied, other ions are also diffused, so thatthe ion implantation process to the rear surface side regions, i.e., thesecond surface side regions of the light reception units is carried outbefore device separation regions in which details have not been formedyet are formed.

At this time, the relatively strong heating process that is carried outfor the subsequent formation of device separation regions can be usedfor diffusing the impurity of the first conductivity-type impurityregions 17 as the second surface 11B side regions, so that there is anadvantage that adding another process is avoided.

Carrying out ion implantation in this stage means that ion implantationis inevitably carried out from the first surface 11A side. In theabove-described Processes (1) through (3), ion implantation is carriedout to the area slightly narrow than the finally implanted area, and bymeans of diffusion by heating processes for subsequent formation ofdevice separation areas, the distribution is made to be gentlyoverlapped. Thereby, density gradient that is gentle in the horizontaldirection also is generated, and it becomes easy to move electrons tothe first surface 11A side regions of the light reception units.

Furthermore, when implanting impurity from the first surface 11A side,if implantation is carried out after formation of device separationregions, the implantation depth is caused to differ between the partswhere the impurity passes the device separation regions and the partswhere the impurity passes the areas other than the device separationareas. If all of the pixels are laid out in the same manner, the problemis relatively small, however, when the circuit configuration is the oneshared by a plurality of pixels as in the solid-state imaging deviceaccording to an embodiment of the invention, because the layout, i.e.the arrangement, of neighboring pixels are different, the variation inthe implantation depths of ions as described above becomes the cause ofgenerating a variation in sensitivity, saturation characteristics, etc.between neighboring pixels. Accordingly, when ion implantation iscarried out from the first surface 11A side, because of theabove-described reason also, it is preferable to carry out the ionimplantation before formation of device separation regions.

Process (4):

Next, as illustrated in FIG. 7A, device separation regions 18 areformed. Here, STI (Shallow Trench isolation) is used, in which a trenchis formed in the semiconductor substrate 11 of silicon, etc. and forexample SiO₂ is buried in the trench. Because it passes through theheating process at about 950° C. on the way, as described above, moreions implanted in the previous processes are diffused.

Process (5):

Thereafter, as illustrated in FIG. 7B, gate electrodes 19 are formedthrough the insulating layer 14.

Process (6):

As illustrated in FIG. 7C, the structures in the first surface 11A sideregions of the light reception units are formed. For example, arsenic,etc. of the first conductivity-type, in this case, of n-type, are ionimplanted to form first conductivity-type impurity regions 20. Then,although not shown, side walls of the gate electrodes 19 are formed, andboron, etc. of the second conductivity-type, in this case n-type, areion implanted and are activated without being diffused so much through alight heating process at bout 850° C. Although not shown, sources anddrains of transistors are also formed in this process.

Process (7):

As illustrated in FIG. 8, wiring layers 23 and 24 are formed above thegate electrodes 19 through an interlayer insulating layer 22, and asupport substrate 32 of silicon, etc. is stuck by means of an adhesive31 of BCB (benzocyclobutene) resin, etc.

Process (8):

Thereafter, the semiconductor substrate 11, i.e., SOI substrate, isreversed, the substrate 13 of the SOI and the insulating layer 12 formedby an embedded oxide film are removed by polishing and etching to exposethe second surface 11B. Further, a thin protective oxide film is formedon the surface of the second surface 11B, and as illustrated in FIG. 9,boron, etc. are ion implanted to the surface on the second surface 11Bside, and activation is carried out by means of laser annealing, etc. toform a second conductivity-type impurity layer 26 of p-type.Furthermore, an oxide film 40 is formed thereupon.

Process (9):

Thereafter, as illustrated in FIG. 10, a protective film 41 consisted ofa silicon nitride film, etc. is formed on the oxide film 40 on thesecond surface 11B, and furthermore, color filters 42 and on-chip lenses43 are formed. The color filters 42 and the on-chip lenses 43 are formedat approximately even intervals in positions corresponding to the secondconductivity-type impurity regions 21 and the first conductivity-typeimpurity regions 20 and 17, which constitute the light reception units.

Here, in the invention, the even intervals need not be complete andstrict even intervals, and it would be sufficient if the evenness is ata level that there is no problem from a practical point of view, andmore specifically, if it is in a range that special signal processingfor correcting variation in the intervals of the light reception unitsis unnecessary.

Further, in the solid-state imaging device according to an embodiment ofthe invention, the arrangements are different between the first surfaceside regions and the second surface side regions of the light receptionunits, that is, between the front surface side regions and the rearsurface side regions of the light reception units, however, it ispreferable that the optimum arrangement is selected as their relativepositional relationship. As an example, as in the above-describedembodiment, when pixels are arranged in units of four pixels, theoptimum arrangement can be selected using the following method.

Suppose that geometric gravity centers in the front surface side regionsof the light reception units for example PDs are arranged at unevenintervals in positions of points p1, p2, p3, and p4 on the coordinateaxes, and those in the rear surface side regions of the light receptionunits are arranged at even intervals in positions of points q1, q2, q3,and q4 on the coordinate axes. In this case, to determine the relativerelationship of the geometric gravity centers between the front surfaceside regions and the rear surface side regions of the light receptionunits, the maximum value pi−qi and the minimum value pj−qj (each of iand j is one of 1, 2, 3, 4) of p1−q1, p2−q2, p3−q3, and p4−q4 have onlyto satisfy; pi−qi=−(pj−qj). This means that the maximum value ofdeviation in the geometric gravity centers between the front surfaceside and the rear surface side of the PDs is made minimum.

In the example of FIG. 5B, the maximum value and the minimum value ofthe deviation in the geometric gravity centers are given by the lightreception units 61 b and 61 c, and the light reception units 61 a and 61d take the values between the maximum value and the minimum value. Thelight reception units 61 b and the light reception unit 61 c are in thesame shape if left and right are reversed, however, if they remain asthey are, the shapes of the light reception unit 61 b and the lightreception unit 61 c relative to the incident light Lb and the incidentlight Lc are different, so that the light reception units 61 b and thelight reception unit 61 c are different in shapes.

Note that it is apparent that this method can be applied to cases otherthan the case that pixels are arranged in units of four pixels.

So far, the description has been made taking the example ofconfiguration that four pixels in the column direction are shared;however, various other configurations have been proposed in the pixelsharing method. For example, the configuration that two neighboringpixels in the column direction are shared as illustrated in FIG. 11 hasbeen known, and also the configuration that two pixels each in thecolumn direction and in the line direction, i.e., four pixels in twolines and two columns, are shared as illustrated in FIG. 12 has beenknown. In FIG. 11 and FIG. 12, the parts corresponding to those of FIG.4 are denoted by the same reference symbols and overlapped descriptionis omitted. The invention can be similarly applied, including the casesof FIG. 11 and FIG. 12, to various solid-state imaging devices sharingpixel circuits by a plurality of pixels. It should be noted that in theexample illustrated in FIG. 11, the wirings 69 are arranged over thelight reception units, however, because the solid-state imaging deviceof the invention is configured as the rear-surface-incident-type device,there should be no problem. In the known front-surface-incident-typedevice, the configuration that wirings cross over the PDs may not beadopted because incident light is hindered. However, by adopting therear-surface-incident-type configuration, the freedom in the wiringarrangement can be increased as described above, so that furtherminiaturization of pixels and circuits becomes possible.

FIG. 13 illustrates an exemplary planer configuration of the lightreception units viewed from the rear surface side, i.e., the secondsurface 11B side, of the solid-state imaging device according to anembodiment of the invention. As illustrated in FIG. 13, in this example,the first conductivity-type impurity regions 17, which are the secondsurface side 11B regions and the incident side regions of the lightreception units 61, are arranged at approximately even intervals. As oneexample, there is shown in FIG. 13 an arrangement example of the firstconductivity-type impurity regions 17 corresponding to respectivecolors, green (G), red (red), and blue (B), in the color solid-stateimaging device for use in a single-CCD camera.

As described above, in the solid-state imaging device according to anembodiment of the invention, making the arrangement of the secondsurface side regions, i.e., rear surface side regions, of the lightreception units at approximately even intervals need not be complete andstrict necessarily, and is sufficient if that is within a range thatthere is no problem from a practical point of view. That is, even if theintervals slightly vary, there would be no problem if the intervals areat such a level that in subsequent signal processing, sampling can betreated as being carried out at even intervals.

Further, although it is preferable that all of the shapes and areas ofthe second surface 11B side regions, i.e., first conductivity-typeimpurity regions 17, of the light reception units 61 are the same,however, if they are arranged at even intervals, all of the shapes andareas need not be necessarily the same.

For example, in FIG. 14, it is configured such that the contact parts 70are arranged between the first conductivity-type impurity regions 17 onthe assumption that the contacts are dropped down to the p-well, etc.from the rear surface side, and an example of a planner shape is shownin which parts of the first conductivity-type impurity regions 17 areomitted. When such a planer shape is taken, the positions of thegravities are not at even intervals in a precise sense. However, evenwhen such configuration is taken, there would be no problem if theconfiguration is in such a level that sampling can be treated as beingcarried out at even intervals in subsequent signal processing.

Also, for example, to align the spectral sensitivities, it is alsopossible as illustrated in FIG. 15 to differentiate the areas of thefirst conductivity-type impurity regions 17 as the rear surface sideregions correspondingly to the positions of the color filters. In theexample illustrated in FIG. 15, although respective areas of the firstconductivity-type impurity regions 17 are different, positions of theirgravities are lined up at even intervals.

For example, when blue sensitivity is hard to be obtained, asillustrated in FIG. 15, only the light reception units 61 correspondingto blue color filters, in this example, the first conductivity-typeimpurity regions 17B, are made with their areas increased, and therebythe blue sensitivity can be increased.

Using the above-described solid-state imaging device according to anembodiment of the present invention, as illustrated in FIG. 16, it ispossible to make an imaging apparatus 100 according to an embodiment ofthe invention.

The imaging apparatus 100 illustrated in FIG. 16 is configured as anelectronic apparatus having the functions of a portable phone, a digitalstill camera, and a video camera, and other imaging functions. Theimaging apparatus 100 includes an imaging optical unit 101, asolid-state imaging device 102, a signal processing unit 103, and atemporary storage unit 105, a display device 106, a recording device107, an operation unit 108, and a power source unit 109, which areconnected with the signal processing unit 103 by a transmission bus line104.

The imaging optical unit 101 includes various lenses, a shutter, adiaphragm, etc., and guides light of an imaging subject to thesolid-state imaging device 102. The solid-state imaging device 102 isthe solid-state imaging device according to the above-describedembodiment of the invention, and photo-electrically converts the lightfrom the imaging subject imaged through the imaging optical unit 101 tobe outputted as a signal. The signal processing unit 103 includes a DSP(Digital Signal processor) for processing digital signals, etc., andcarries out formatting processing, etc. on image signals outputted fromthe solid-state imaging device 102 to be converted to data fordisplaying and recording.

The temporary storage unit 105 includes a RAM (Random Access Memory),etc., and temporarily stores image data processed by the signalprocessing unit 103. The display device 106 includes a liquid crystaldisplay, etc., and displays the image data processed by the signalprocessing unit 103. The recording device 107 includes a flash memory,an EPROM (Erasable Programmable ROM), an HD (hard disk), etc., andrecords image data. The operation unit 108 includes a shutter button forinputting a control signal controlling the operation of the imagingapparatus 100 from outside, various function keys, a cursor, etc. Thepower source unit 109 supplies the operation power to theabove-described units of the imaging apparatus 100.

By configuring the imaging apparatus 100 using the solid-state imagingdevice according to the above-described embodiment, it is possible tocarry out signal processing with sampling at even intervals, so that itbecomes possible to avoid signal processing from becoming complicated.

It should be noted that the configuration of the imaging apparatus 100is not limited to the above-described one, and various otherconfigurations may be adopted.

As described above, according to the solid-state imaging device and theimaging apparatus of the invention, with the provision of a common pixelcircuit for a plurality of pixels, while increasing the number of pixelsas the pixels are miniaturized, by arranging the rear surface sideregions of the light reception units at approximately even intervals asthe rear-surface-incident-type device, the incident light can be sampledat even intervals.

Further, the range of choices of the signal processing unit, forexample, a DSP, is expanded, and shading correction and other signalprocessing are avoided from becoming complicated. As a result, thesignal processing becomes light, and images become clean. Further,because of sampling at even intervals, the characteristics of pixels arenot decreased, and relatively clean images can be imaged.

As described above, even if PDs are arranged at uneven intervals becauseof the layout of pixel sharing, the incident light can be sampled ateven intervals.

Thereby, in contrast to the known solid-state imaging devices in whichPDs are arranged at uneven intervals, the following advantages can beobtained.

a) Signal processing is simple and concise, and as a result, arelatively clean image can be provided.

b) It is not necessary to design the signal processing unit, forexample, a DSP system, for each product of CMOS sensors, and it is notnecessary to differentiate the system of the signal processing unitbased on the arrangement of pixels.

c) Reproducibility of intervals of stripes and coloring manner whenstripe patterns have been imaged is satisfactory.

d) Because many choices are available for signal processing ICs, theapparatus configuring method is diversified.

e) How shading comes out does not change due to uneven intervals of theincident light reception units. For example, when a white subject isimaged, it does not occur that the upper edge and the lower edge arecolored and moreover colored in different colors such that correctionbecomes difficult, and it is avoided that signal processing becomescomplicated.

Also, in the known solid-state imagine device, with respect to themethod of solving the inconveniences caused by that pixel circuits areshared and that the light reception units are arranged at unevenintervals, when the invention is applied, the following effects areproduced.

f) It is not necessary to put a limitation to the shape of the openingand it can be avoided that the area of the light reception unit isdecreased.

g) It can be avoided that the characteristics of the pixel circuit suchas conversion gain, etc. is cause to decrease.

h) Because the area of the light reception unit can be kept as comparedwith the front-surface-incident-type device, lowering of the sensitivitycan be avoided.

i) Although each time when newly designing a solid-state imaging devicesuch as a CMOS sensor, etc. for a different pixel size, works werenecessary such as reselecting materials different in refractive indexand redesigning the shape of an in-layer lens, such complicated worksbecome unnecessary.

It should be understood by those skilled in the art that variousmodifications, combinations, sub-combinations and alterations may occurdepending on design requirements and other factors insofar as they arewithin the scope of the appended claims or the equivalents thereof.

1. A solid-state imaging device comprising: a semiconductor substratewith a first surface and a second surface opposite the first surface; aplurality of light reception regions formed in the semiconductorsubstrate, respectively having first surface side regions formed in afirst surface side part of the semiconductor substrate and secondsurface side regions formed in a second surface side part of thesemiconductor substrate; and a pixel circuit formed on the first surfaceside of the semiconductor substrate and shared by the plurality of lightreception regions, wherein the second surface side, opposite the firstsurface side where the pixel circuit is formed, of the semiconductorsubstrate is made a light incident side of the light reception regions,and wherein the second surface side regions of the light receptionregions formed in the second surface side part of the semiconductorsubstrate are arranged at approximately even intervals and the firstsurface side regions of the light reception regions formed in the firstsurface side part of the semiconductor substrate are arranged at unevenintervals, respectively, and the second surface side regions and thefirst surface side regions of the light reception regions are joinedrespectively in the semiconductor substrate so that the light receptionregions extend from the second surface side to the first surface side ofthe semiconductor substrate.
 2. The solid-state imaging device accordingto claim 1, wherein depths of the second surface side regions of thelight reception regions are from 1 μm to 5 μm from the second surface ofthe semiconductor substrate.
 3. The solid-state imaging device accordingto claim 1, wherein the second surface side regions of the lightreception regions are formed by ion implantation from the first surfaceside of the semiconductor substrate.
 4. The solid-state imaging deviceaccording to claim 3, wherein the ion implantation is carried outseveral times while changing energy, and densities of the first surfaceside regions are higher than densities of the second surface sideregions.
 5. The solid-state imaging device according to claim 3, whereinthe ion implantation is carried out before formation of deviceseparation regions.
 6. An imaging apparatus comprising: a solid-stateimaging device; an imaging optical unit guiding light from an imagingsubject to the solid-state imaging device; and a signal processing unitprocessing an image signal outputted from the solid-state imagingdevice, wherein the solid-state imaging device includes, a semiconductorsubstrate with a first surface and a second surface opposite the firstsurface; a plurality of light reception regions formed in thesemiconductor substrate, respectively having first surface side regionsformed in a first surface side part of the semiconductor substrate andsecond surface side regions formed in a second surface side part of thesemiconductor substrate; and a pixel circuit formed on the first surfaceside of the semiconductor substrate and shared by the plurality of lightreception regions, wherein the second surface side, opposite the firstsurface side where the pixel circuit is formed, of the semiconductorsubstrate is made a light incident side of the light reception regions,and wherein the second surface side regions of the light receptionregions formed in the second surface side part of the semiconductorsubstrate are arranged at approximately even intervals and the firstsurface side regions of the light reception regions formed in the firstsurface side part of the semiconductor substrate are arranged at unevenintervals, respectively, and the second surface side regions and thefirst surface side regions of the light reception regions are joinedrespectively in the semiconductor substrate so that the light receptionregions extend from the second surface side to the first surface side ofthe semiconductor substrate.
 7. A production method of a solid-stateimaging device, comprising steps of: implanting impurity of a firstconductivity-type from a first surface side of a semiconductor substrateto form second surface side regions of light reception regions atapproximately even intervals in a second surface side part of thesemiconductor substrate; forming device separation regions in a firstsurface side part of the semiconductor substrate; forming gateelectrodes on the first surface of the semiconductor substrate;implanting second conductivity-type impurity on the second surface sideregions of the light reception regions from the first surface side ofthe semiconductor substrate to form first surface side regions of thelight reception regions at uneven intervals in the first surface sidepart of the semiconductor substrate; forming an interlayer insulatinglayer and wiring layers on the first surface of the semiconductorsubstrate; and etching the semiconductor substrate from the secondsurface side opposite the first surface of the semiconductor substrateto expose the second surface side regions of the light reception regionsarranged at approximately even intervals in the second surface side partof the semiconductor substrate, wherein the step of implanting impurityfrom the first surface side of the semiconductor substrate to form thesecond surface side regions of the light reception regions is carriedout before the step of forming the device separation regions.